ANTLR3 树语法：循环在输入'EOF'处不匹配任何内容

Question

我正在尝试创建我的第一个ANTLR3树语法，但我一直遇到同样的问题。解析器的输出是:

$ echo 'foo, bar' | ./run.sh 
foo bar
TreeGrammar.g: node from line 0:0 required (...)+ loop did not match anything at input  'EOF'
Exception in thread "main" java.lang.NullPointerException
    at Driver.main(Driver.java:29)

输出清楚地表明stage-1解析器产生正确的令牌('foo'和'bar')。不知何故，阶段2的树解析器拒绝解析阶段1的结果。由于代码是非常基本的，它一定是我的一些简单而愚蠢的疏忽;-)

下面是我的简单测试代码:

Grammar.g:

grammar Grammar;
options {
    output = AST;
}
statement: word (','! word)* EOF!;
word: ID;
ID: ('a'..'z'|'A'..'Z')+;
WS: (' ' | 't' | 'n' | 'r')+ { $channel = HIDDEN; } ;

TreeGrammar.g:

tree grammar TreeGrammar;
options {
    tokenVocab = Grammar;
    ASTLabelType = CommonTree;
    output = template;
}
statement: word+;
word: ID;

Driver.java:

import java.io.*;
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Driver {
    public static void main(String[] args) throws Exception {
        FileReader groupFileR = new FileReader("Template.stg" );
        StringTemplateGroup templates = new StringTemplateGroup(groupFileR);
        groupFileR.close();
        ANTLRInputStream input = new ANTLRInputStream(System.in);
        GrammarLexer lexer = new GrammarLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        GrammarParser parser = new GrammarParser(tokens);
        GrammarParser.statement_return result = parser.statement();
        CommonTree t = (CommonTree)result.getTree();
        System.out.println(t.toStringTree());
        CommonTreeNodeStream nodes = new CommonTreeNodeStream(t);
        nodes.setTokenStream(tokens);
        TreeGrammar walker = new TreeGrammar(nodes);
        walker.setTemplateLib(templates);
        walker.statement();
        TreeGrammar.statement_return r2 = walker.statement();
        StringTemplate output = (StringTemplate) r2.getTemplate();
        System.out.println(output.toString());
    }
}

Answer 1

假设你的Stringtemplate组是正确形成的，你的问题很可能是你遍历 AST两次:

    walker.statement();
    TreeGrammar.statement_return r2 = walker.statement();

。，你调用walker.statement()两次。这是(第一个)错误告诉你的:

TreeGrammar.g: node from line 0:0 required (...)+ loop did not match anything at input 'EOF'

您使用walker.statement()消耗一次输入，导致节点流处于结束(EOF)，然后您再次调用walker.statement()，它期望再次行走word+，但只剩下EOF。